[ntp:questions] how do I lock in average frequency correction

Dave Hart hart at ntp.org
Mon Feb 13 08:25:17 UTC 2012


On Mon, Feb 13, 2012 at 07:56, David Woolley
<david at ex.djwhome.demon.invalid> wrote:
> Terje Mathisen wrote:
>
>> But doesn't the HAL clock also support _both_ a fixed/baseline clock
>> frequency adjustment, and a temporary adjustment to be applied over the next
>> N time slices/seconds?
>
> Yes.  My assumption of only one mechanism may be unsound.

I beg to differ.  The only interface for slewing the clock exposed by
Windows is SetSystemTimeAdjustment, which changes the clock rate with
wide latitude and persistently (until changed again).  There is no 500
PPM cap, beware of computers that do what you ask and not what you
want :)

As an aside, I don't find it useful to talk about the HAL as a
separate entity.  Unless you're a hardware engineer doing novel work
on systems which will run Windows, it's just an implementation detail
of the Windows OS.  There's nothing preventing a new release of
Windows from expanding the HAL/kernel interface to accommodate any
desired new functionality in the kernel, because MS controls both
sides of the interface and distributes matched HALs and kernels with
each release.

Now to find another thread to flood...

Cheers,
Dave Hart


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